Study on strength and deformability of Hawkesbury sandstone subjected to cyclic loading

Abstract

An experimental investigation was carried out on the Hawkesbury sandstone to study the mechanical rock behaviour (i.e. strength and deformability) during uniaxial and triaxial cyclic compressive testing. Axial load, confining pressures and axial and lateral deformations were measured continuously from start of loading until post-peak state. Cyclic tests were carried out at different confining pressures, stress levels and unloading amplitudes. Results indicate that damage increases with an increase in unloading stress level and unloading amplitude. It was observed that fatigue life of a confined specimen is longer than fatigue life of a sample without confinement. In addition, in cyclic loading tests, a relatively uniform accumulation in axial, lateral and volumetric strain follows by a rapid increase in strain as the sample headed towards failure. Moreover, during cyclic loading a continuous degradation in the tangent Young’s modulus until beginning of large plastic deformation was observed and then it decreased rapidly within few cycles before the failure. Poisson’s ratio increased during cyclic loading. This trend became very significant when unstable cracks begin to initiate inside the sample.